1. Field of the Invention
The present invention relates to an activating apparatus for vehicle passenger protection devices.
2. Description of the Related Art
Various methods for determining likelihood of rollover of a vehicle have been proposed, as disclosed in, for example, Japanese Patent Laid-open Publication (JP-A1) No. 2001-260780. According to the disclosed vehicle rollover likelihood determining method, a threshold line is set on a two-dimensional map drawn with the roll angle and roll angular rate of a vehicle as parameters, and the likelihood of a vehicle rollover is determined based on whether or not a hysteresis line of the actual roll angle and roll angular rate of the vehicle crosses the threshold line from a non-rollover area to a rollover area. The result of the vehicle rollover likelihood determination is used for deployment control of a curtain airbag module or a side airbag module.
In the disclosed vehicle rollover likelihood determining method, particular note is taken of the fact that when the lateral slip speed is high, the so-called xe2x80x9ctrip-overxe2x80x9d type rollover is likely to occur; the threshold line is moved to approach the original point of the two-dimensional map as the lateral slip speed of the vehicle increases, thereby enabling early determination of likelihood of a vehicle rollover.
Even in case of the xe2x80x9ctrip-overxe2x80x9d type rollover, however, if there is no occupant present on the navigator""s seat, it is desirable for a curtain airbag module or the like protection device on the navigator""s seat side to be deployed not at the same time as deployment of a curtain airbag module on the driver""s seat side, but at the time the roll angle of the vehicle becomes large to some extent because a delayed deployment of the navigator""s seat side curtain airbag module can effectively protect the driver from crashing through a window of the navigator""s seat side. This means that the known vehicle rollover likelihood determination method discussed above cannot activate passenger protection devices, such as curtain airbag modules or side airbag modules, in the vehicle at the right time.
It is accordingly, an object of the present invention to provide an activation apparatus for passenger protection devices in a vehicle, which is capable of activating the passenger protection devices at the right time in accordance with the position of occupants in the vehicle.
To achieve the foregoing object, according to the present invention, there is provided an activating apparatus for passenger protection devices in a vehicle, comprising: a roll condition detecting means for detecting a roll condition of the vehicle; activation determining means for, on the basis of the roll condition detected by the roll condition detecting means, determining likelihood of a vehicle rollover, and on the basis of a result of the determination, performing determination on the activation of a passenger protection device on a driver""s seat side and a passenger protection device on a navigator""s seat side of the vehicle; occupant detecting means for detecting an occupant in the vehicle; and determination condition changing means incorporated in the activation determining means for, when only the presence of an occupant on a driver""s seat has been detected by the occupant detecting means, changing determination conditions relating to the vehicle rollover that are used for the determination of activation of the passenger protection device on the navigator""s seat side, into conditions that make it difficult for the activation determining means to render a decision that a vehicle rollover is imminent.
With the activation apparatus thus arranged, when the navigator""s seat is not occupied by a passenger, the vehicle rollover-related determination conditions are changed to conditions that make it difficult to render a decision that a vehicle rollover is imminent, so that the passenger protection device on the navigator""s seat side is activated after activation of the passenger protection device on the driver""s seat side.
In one preferred form of the invention, the roll condition detecting means comprises roll angular rate detecting means for detecting a roll angular rate of the vehicle, and roll angle detecting means for detecting a roll angle of the vehicle or roll angle calculating means for calculating by integration a roll angle of the vehicle from the roll angular rate detected by the roll angular rate detecting means, and the determination condition changing means, when the presence of an occupant on the driver""s seat and the presence of an occupant on the navigator""s seat have been detected by the occupant detecting means, allows the activation determining means to perform determination of the likelihood of a vehicle rollover based on the roll angle and the roll angular rate, and when only the presence of an occupant on the driver""s seat has been detected by the occupant detecting means, allows the activation determining means to perform determination of the likelihood of a vehicle rollover based solely on the roll angle.
According to the vehicle rollover likelihood determination based on the roll angle and the roll angular rate, it is possible to estimate a feature roll angle from the current roll angular rate of the vehicle. On the other hand, the vehicle rollover likelihood determination based solely on the roll angle cannot infer a feature roll angle from the current roll angle. Thus, the first-mentioned rollover likelihood determination can render or provide, at early stages of a rollover event, a decision that such vehicle rollover is imminent. In the case of the second-mentioned rollover likelihood determination, however, the same decision can be provided at a later time than that of the first-mentioned rollover likelihood determination.
Thus, as compared with a mode of activation effected simultaneously with the activation of the passenger protection device on the driver""s seat side, the passenger protection device on the navigator""s seat side is activated at the right time (namely, with a time delay) in view of the position of an occupant in the vehicle.
In another preferred form of the present invention, the roll condition detecting means comprises roll angular rate detecting means for detecting a roll angular rate of the vehicle, and roll angle detecting means for detecting a roll angle of the vehicle or roll angle calculating means for calculating by integration a roll angle of the vehicle from the roll angular rate detected by the roll angular rate detecting means, and the activation determining means comprises rollover determining means having a two-dimensional map with roll angle and roll angular rate of the vehicle as parameters, the two-dimensional map having a boundary line set to separate a rollover region in which a vehicle rollover can occur and a non-rollover region in which the vehicle rollover cannot occur, and the rollover determining means performs determination of the likelihood of a vehicle rollover by putting a value of the roll angle and a value of the roll angular rate into the two-dimensional map.
By virtue of the boundary line set on the two-dimensional map to separate the rollover region and the non-rollover region, the likelihood of a vehicle rollover can readily be determined by a region in which the respective values of the roll angle and the roll angular rate belong.
Preferably, the determination condition changing means sets a second boundary line with a larger threshold value than the first-mentioned boundary line onto the two-dimensional map that is determined by shifting the first-mentioned boundary line in a direction to mitigate the likelihood of a vehicle rollover.
By thus shifting the boundary line to set a higher threshold second boundary line when no passenger is present on the navigator""s seat, activation of the passenger protection device on the navigator""s seat side is deferred until both the roll angle and the roll angular rate of the vehicle become large or increase to some extent. With this delayed activation, the passenger protection device on the navigator""s seat side is activated at an appropriate time to the occasion where no passenger is present on the navigator""s seat.
In still another preferred form of the present invention, the activation determining means further comprises variation calculating means for calculating a variation in roll angular rate with time, and the activation determining means performs determination of activation of the protection device on the driver""s seat side based on the variation in roll angular rate calculated by the variation calculating means and a result of the determination performed by the rollover determining means.
In a particular form of rollover where the roll angular rate is high at early stages of a rollover event, a variation in roll angular rate with time becomes large. Accordingly, if the passenger protection device on the driver""s seat side is activated when a large roll angular rate variation occurs, this will achieve activation of the driver""s seat side passenger protection device at early stages of rollover event. For the passenger protection device on the navigator""s seat side, activation determination using the roll angular rate variation is not effected with the result that early activation of the navigator""s seat side passenger protection device does not occur.